Call management in a collaborative working network

ABSTRACT

A programmable workstation for collaborative working in a network comprises a conventional operating system and network control layer for controlling physical routing of data between nodes. A collaborative application subsystem which interfaces with application programs is responsive to a predetermined call from a collaboration call manager to establish the call manager at the node to handle incoming events which are not specific to any application program instances at the node.

FIELD OF THE INVENTION

1. Description

This invention relates to call management in a collaborative workingnetwork and more specifically to a programmable workstation and a methodfor use in such a collaborative working environment.

2. Background of the Invention

Personal computers are now widespread throughout the business communityand many are able to intercommunicate, either through fixed connectionse.g. local area networks, or through dynamically established links e.g.ISDN or async lines over the public switched telephone network.Increasingly, these connected personal computers can be used to enhancecollaborative working between remote individuals; a typical examplebeing the use of desk top conferencing software. Successfulcollaborative work generally requires more than a simple data linkbetween the participants; voice capabilities are normally essential andvideo links are frequently required. Thus remote collaborative workingcan often be regarded as an extension to the traditional telephonecall--it being enhanced with the data and programs available at thedesktop via the personal computer--and, on occasions, enriched withvideo services.

A broad spectrum of collaborative applications can be envisaged, rangingfrom utilities taking advantage of the data and applications on aworkstation, e.g. sharing of screen windows and files, through to newcollaborative applications designed to meet the needs of specificclasses of remote user e.g. just-in-time education, remotepresentations, executive broadcasts or help desk. The commonrequirements behind these examples are:

the support of a wide variety of personal computer platforms--bothhardware and software.

operation over the existing communication networks.

group communications and multi-media data services.

The behaviour of a desk top conferencing system, particularly the way inwhich the system reacts to incoming calls, is usually determined by thesuppliers of the system software. The conventional view of real-timedesk top conferencing makes a distinction between the system functions,such as setting up and tearing down calls, and application functions,such as sending and receiving data. Thus while applications (such as ashared electronic chalkboard) may be aware of events such as the startand end of calls, they are unable to affect the way these events arehandled in detail. For example, the barring of incoming calls isnormally regarded as a system function which can be toggled on and offby time user and perhaps, via an API call, by an application program.

SUMMARY OF THE INVENTION

Accordingly, the invention provides a programmable workstation forcollaborative working in a network of workstations forming tile nodes ofthe network, the network being connected by physical links for thetransmission of data between nodes;

the workstation comprising an operating system;

a network control program layer, running on the operating system, forcontrolling physical routing of data between nodes; and

a collaborative application subsystem for interfacing with applicationprograms running on time workstation and responsive to a predeterminedapplication program call from a collaboration call manager program toestablish the collaboration call manager program at the node to handleincoming events which are not specific to any application programinstance at time node.

The invention further provides a method of collaborative working in anetwork of programmable workstations forming the nodes of a networkconnected by physical links for the transmission of data between nodes,the method comprising in response to a predetermined application programcall from a collaboration call manager program running on theworkstation, establishing time collaboration call manager program attile node to handle incoming events which are not specific to anyapplication program instance at the node.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only withreference to FIGS. 1-17 of the accompanying drawings, in which:

FIG. 1 shows two programmable workstations connected by a network;

FIG. 2 illustrates the relationship between the support program shown inFIG. 1 and other software components on a workstation;

FIG. 3 illustrates applications being shared between nodes;

FIG. 4 shows the sharing sets resulting from the application sharingillustrated in FIG. 3;

FIG. 5 shows applications linked by a data communication link orchannel;

FIG. 6 shows applications linked by channels to provide serialization ina shared drawing board;

FIG. 7 shows the use of a synchronizing channel to provide datasynchronization;

FIG. 8 shows the structure of a sending port at one end of a channel;

FIG. 9 shows the use of receiving ports to provide serialization;

FIG. 10 illustrates the components of the support program;

FIG. 11 shows how an application window at one node may be displayed ata remote node;

FIG. 12 illustrates the sequence of events resulting from a call to thesupport structure;

FIG. 13 illustrates exemplary utilities provided on top of thecollaborative support system;

FIG. 14 illustrates the flow of requests and calls to initiate andterminate sharing between/two applications using the call manager;

FIG. 15 illustrates the user interface of the call manager;

FIG. 16 illustrates an example of the arrangement of calls between fournodes;

FIG. 17 illustrates the six main states of the call manager and thetransitions between them.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 are shown two programmable workstations 10 and 12 connected bylink 11 in a network, such as a LAN or WAN. The principal components ofthe workstations are conventionally described as layers, starting withthe hardware 13. The hardware which is not illustrated in detail,consists of a processor unit with main memory, secondary storage such asa disk file, a display unit and input/output devices such as keyboardand mouse. Device support software 14 enables the hardware devices tofunction within a known operating system 15, such as IBM's OperatingSystem/2 (OS/2).

Also part of a conventional workstation, when used in a network, isnetworking software 16 for supporting connection to the network 11 andcommunication over the network between workstations. Typical networkingsoftware 16 could be the Netbios program product from IBM. Up to thispoint all that has been described is a conventional networkingworkstation capable of executing application programs 18.

In order to implement the present invention, each workstation alsoincludes collaborative application support system software 17 whichfacilitates the development of application programs for creating adistributed collaborative working environment. In this environment,end-users of the workstation may communicate with users of otherworkstations in the network over multi-media channels and may workcollaboratively on shared data and tasks.

The overall structure of support system 17 in relation to other softwarecomponents of the workstation with which it interfaces directly is shownin FIG. 2. Further details of the internal structure of the supportsystem are shown in FIG. 10. Broadly speaking, the main functionalcomponents of system 17 lie between two interfaces 20 and 21,illustrated by dashed lines.

An application programming interface 20 allows applications 18 torequest support services. A device driver interface 21 allows the systemto support an extensible range of software and hardware communicationssubsystems through device drivers such as token ring driver 25, ISDNdriver 6, RS232 driver 27 and other device drivers 28. Link supportmodules 228, 229 interface with the device drivers. These arereplaceable, (FIG. 10 shows only a possible selection) depending on thehardware options available at the workstation, and serve to isolate thesupport system from needing to know precisely which hardware is present.Through an implicit resources interface, (not illustrated) details ofthe communications , network, such as node addresses and directory datamay be requested by both the support system, the applications and thedevice drivers from resource files 29.

The API 20 allows applications 18 to initiate peer applications andshare resources, on a variety of hardware and soft:ware platforms,located on nodes across a diverse and complex communications networks.It allows them to define multiple dedicated logical data channelsbetween shared applications, suitable to a broad range of multi-mediatraffic, independently of tile structure of the underlying physicalnetwork. It allows them to serialise, synchronise, merge or copy thedata streaming between shared applications. It also allows them tosupport a range of attached devices and to allow the interception andredirection of the device data.

The support system includes other components to assist applicationdevelopment such as an extensible set of logical devices 30, interfacingto external applications and devices. Also provided is a set of end-userutilities, written to the API (not illustrated), which can also invokedfrom applications through a command interface.

Network, nodes and applications

At the highest level, the programming model presented by the APIconsists of a communicating set of nodes. A node is the addressableentity representing a user, and comprises an instance of tile supportsystem software, and a set of resources such as application programs,data etc. Usually a node is typically a dedicated programmableworkstation 10, capable of communicating with its peers; in a multi-usersystem a node is associated with each user.

Nodes are either supported nodes or non-supported nodes; a supportednode is one where the support system software 17 is being executed. Acollection of inter-communicating supported nodes is called a supportednetwork.

Nodes are identified by name; ideally all node names should be uniquebut duplicates can be tolerated as long as their associated nodes arenever required to inter-communicate. The choice of node naming scheme isnot directly relevant to the present invention, although a hierarchicalsystem such as that defined by the Internet protocol has many benefits.It is fundamental to the architecture that a node can dynamically joinor leave the network.

Nodes can contain logical devices 30. A logical device is a softwareextension to the support system that allows an application to manipulateor manage software or equipment, in a manner consistent with otherentities in the architecture. There is an extensive range of possiblelogical devices including: presentation windows, printers, disk drives,modems, and application programs.

Multiple applications can be executed at a node, subject to theconstraints imposed there by the operating and windowing system.Applications are either aware or unaware; an aware application uses theservices of the API; an unaware application does not. Both aware andunaware applications will generally be executing simultaneously at anode.

When the support system is fully active at a mode, one particular awareapplication must be running at that node. This application plays aunique role at that node and is known as call manager 32. Many callmanagers may be available for execution at a particular node but onlyone can execute at a time. The distinguishing feature of a call manageris that it responds to certain events generated by the support system;for example, it resolves any requests that are not directed specificallyat an instance of an application, and optionally it may also handleresource management for the node. Call manager responsibility can betransferred from one call manager to another; also the role can becombined with user application function if that is appropriate.

The support software 17 may request that the resources of one node aremade available for communication between two other nodes; this is termedpassive operation and permission is controlled by the call manager atthe passive node. As an example, consider two nodes A and B on a LAN,with a third node C connected to B by an asynchronous communicationslink. If applications at A and C wish to communicate, the traffic willneed to be routed via B. The consent of the call manager at B isrequired for this use of its node.

Aware applications can share data and resources with other awareapplications at the same or different nodes. A collection ofapplications sharing is called a sharing set. An aware applicationinitiates a share request, naming an application sharing set, a targetapplication and a destination node. This request is first passed by thesupport software to the call manager at the sending node, which willtypically transfer it to the call manager at the destination node.Usually this second call manager will launch the requested applicationand the source application will be informed. The participation of thecall managers in this process allows both local control of the sharingprocess and other actions to be initiated if necessary. The callmanagers play a vital role in resolving the names used by applicationsto idnetify other nodes and applications. The sharing mechanism can becascaded; for example, if two applications are already sharing, one ofthem can initiate a share with a third application naming the samesharing set, with the result that all three applications are thensharing with each other.

Applications may also make local share requests on behalf of otherapplications thereby allowing membership control of the sharing set tobe delegated. Facilities exist for either the issuer, or the target ofthe share request, to name the application sharing set. These names arenot required to be unique: thus multiple sharing sets with the same namecan exist.

Individual applications can cease sharing at any time, withdrawing froma sharing set; the other applications in the set are informed of thewithdrawal. FIG. 3 shows a number of applications A-E sharing. Thisresults in two sharing sets, irrespective of the order in which theshares were requested, as illustrated in FIG. 4.

Communications, channels and ports

As illustrated in the schematic example of FIG. 5, applications in asharing set such as 40, 41 and 42 can establish data communication linkswith each other known as channels. Channels such as 43 and 44 arelogically dedicated and uni-directional pipes, with applicationspecified transmission characteristics. A channel is always defined bythe sending application and it goes from a sending application to areceiving application. The ends of channels are known as ports; thus allchannels have one sending port and one receiving port. A sending portsuch as 45 sends data packets down the channel; a receiving port such as46 receives data packets from the channel in the order in which theywere sent. There may be no direct mapping between the logical channelstructure seen by the aware applications and the physical communicationnetwork in existence between the nodes.

An application may establish multiple channels to another application asa convenient way to separate data traffic of different types. The systemnetwork manager 31, FIG. 2 may map some or all of the logical channelson to a single physical link such as link 11, FIG. 1 but this will beinvisible to the application.

Channels have a number of quality of service characteristics, initiallynegotiated with the support system 17 during the creation process, whichallow data transmission characteristics to be tailored to tilerequirements of the expected traffic. These characteristics includeencryption, compression hints. Encryption allows time data to beencrypted during transmission along tile channel; compression hintsallow the system the option of compressing the data over narrowbandwidth links.

Quality of service parameters are defined according to signal type,which distinguishes analog from digital data. They need not be specifiedexplicitly, but can be notified to the support system in terms of dataclasses. This mechanism allows video channels, voice channels and otherdata channels to be sensibly established. Channel characteristics can bere-negotiated after channel creation. The data transmissioncharacteristics are implemented in the real network by means of timedata transformation manager 32, FIG. 2 in response to thecharacteristics specified in the channel creation calls over the API.

Four types of channel are supported: standard, merged, synchronous andserialised. Standard channels are the default case; the other types areused in conjunction with collections of channels, known as channel sets.Through a merged channel set data packets are combined from multiplechannels and delivered to each receiving application through a singleport. There is no guarantee that each application receives all the datapackets in the same sequence, only that each application receives allthe packets. Through a serialising channel set data packets are combinedfrom different channels, serialised, and delivered to each applicationsuch that each receiving port receives the same sequence of data.Through a synchronising channel set data is synchronised, so that thedata packets on separate channels are tied together in time (for examplevoice with video), but delivered through the individual ports belongingto the channels.

An example of data serialisation is illustrated by a shared drawingboard application illustrated in FIG. 6. Two identical applications, Aand B (50 and 52), allow their users to draw on a single shared surface.In order that the users at A and B see identical results, all thedrawing orders at A must be sent to B via ports 53 and 54, and viceversa via ports 55 and 56, in such a way that the sequence processed atA and B is identical. This is accomplished by each transmitting theirown data both to each other and to themselves, over two channels 57 and58 which are members of a common serialising channel set 59.

With reference to FIG. 7, data synchronisation is illustrated by anapplication A (60), that needs to send lip-synchronised video and voiceto application B (61). Two channels 62 and 63 are used for thetransmission, each being a member of the same synchronising channel set64.

Channels can be explicitly created by an API call to the support system,specifying the required channel characteristics, and new channels canalso be added to an existing port. The latter mechanism allows a port tobe shared across channels belonging to different channel sets; forexample data can be sent from a single port to one set of destinationsbelonging to a merged channel set, and to a second set of destinationsbelonging to a serialised channel set. Digital channels and analogchannels cannot be members of the same channel set. A channel can bedeleted, the channel being uniquely identified by specifying its sendingand receiving ports.

Channels can be implicitly created as a consequence of an applicationbeing, or becoming, a member of an application sharing set. For example,if unshared applications already have a merged or serialized channel,and the channel set name iused is identical across these applications,then when the applications share with each other, the additionalchannels required will be created automatically. Applications arenotified of channels implicitly created in this way.

Ports have an assigned connect type: event, command or null. Event portsgenerate an event when data is either available or is required; commandports allow the application to drive the receipt or supply of data tothe port. Null ports are reserved for ports that are unable to supplydata to an application e.g. ports associated with analogue channels,such as the sending port of a video camera. Ports can be controlledthrough "signal₋₋ port" commands sent to their port event handler. Thesecan be issued to the local port and can be passed to any other port inthe channel. Normally, the singal commands for channel ports will besent to the port event handler of the application either supplying orreceiving data, and may be used for example to stop, start, decrease orincrease the data flow. The order of signals between a source and targetis maintained. Signals sent to receiving ports in a serialising channelset are serialised themselves, so that all sources receive the samesequence of commands. Other typical signals are "rewind" or "pause" to atape drive, or "change paper size" to a printer device.

User exits can be optionally associated with ports. This allowsmonitoring or manipulation of the data, after it has been supplied to asending port, or before being presented by a receiving port. In the caseof synchronised channels, synchronisation is performed from after thedata leaves the sending port user exit, and up to the data beingpresented to the receiving port user exit.

The overall structure of a standard sending command port is shown inFIG. 8. In response to a "send₋₋ data" command from an application, datais queued in a buffer 71 of port 70. The application empties the bufferto send data asynchronously over a channel 73 via a user exit 72.Incoming "signal₋₋ port" commands are received by the port event handler74, independently of channel 73 on line 75 and can be retransmittedoutwardly on line 76.

Receiving ports are effectively the mirror image of the corresponding*sending port. For a standard receiving event port the structure issimilar, but in this case the event handler processes both the data andthe port commands.

The situation is more complex when synchronisation is involved. In thiscase a standard receiving buffered port must be modified by theinclusion of the synchronisation process on the incoming channel priorto the user exit and the buffer.

Serialisation logically involves the collection of all events in acentral point, followed by the broadcast of each event to all thedestinations for that event. Diagrammatically, this is represented byFIG. 9 for the case of two ports A and B on channels 80 and 81,serialising their output at 82 and 83 to port C (84) and another port(not shown) in serialising process 85. Serialisation can be implementedat a single central point with all data being sent there forserialisation and subsequent distribution; alternatively theserialisation process itself can be distributed.

A receiving port can cause the sending port to stop sending data downthe channel, with the option to either discard or deliver the remainingdata in the channel. Suspended data transmission can be resumedsubsequently.

An alternative method of application inter-communication, avoiding theuse of channels and ports, is provided through a "signal" command whichallows control information to be sent between applications.

Ports are associated with a data class which specifies data type anddata sub-type. The data type identifies the nature of the data, e.g.voice, video, file etc. and also distinguishes analogue from digitaldata. The data types are further subdivided according to the preciseformat of the data; thus examples of voice sub-types are G.711, G.721,G.722.

The data class may be queried by an application to obtain the dataformat, independently of the data stream itself, without relying onother applications. Additionally, the data type may be different at thesending and receiving ports, with Lakes performing the conversions belowthe API.

Certain characteristics of ports and channels can be changed after theyhave been initially established; for example, quality of service, dataclass and compression hints. This provides the flexibility for anapplication to modify its communications usage during execution; anexample being the temporary degradation of video quality to improve fileexchange performance.

Ports can be connected together to establish extended communicationlinks, so that an application may route its inputs through to anotherapplication for processing. When ports are connected in this way, andproviding user exits have not been established, no further applicationinvolvement is required after the routing has been established. Thisallows the streaming of data between applications and devices.Connection is permitted between channels in different channel sets, ofdifferent types, having different quality of service characteristics, ofdifferent data class or different connect types (unless one of the portsis null), provided only that one port is sending and one port isreceiving. Connected ports can also be welded, so that the connection ispermanent and persists even when the local application has terminated.The channel behaves in all respects as though it had been originallycreated from its source directly to its destination. Any user exitswhich may be present are removed.

Logical Devices

Logical Devices 30 (FIG. 2) are supported by the support system toenable (i) easier access to system resource and devices, such asclipboard, DDE, printer and video devices, (ii) unaware applications tobe used for collaborative working, for example by giving access to thewindow contents and file activity of an unaware application, and (iii)end to end data streaming without application involvement. Frequentlyused devices include: video capture, video playback, audio playback etc.and facilities are provided for additional devices to be defined.

Logical devices are identified by type; the type names are local to anode. When opened, they present a port to the application; a singlelogical device can have multiple ports, moreover a device cansimultaneously present ports to different applications at the same node.The relevant API call to open a port allows characteristics to beestablished, peculiar to that device, for example the data formats to beused. Opened logical devices can be controlled through commands sent tothe signal port, the commands being specific to the particualr logicaldevice. Typical commands to a device port are rewind or pause to a tapedrive. The device status, for example whether data is available, canalso be queried.

Devices are exactly like channel ports, except that no user exit ispresent. Applications can connect ports on logical devices to a channelport; this enable data to flow to or from the device and across thechannel. This data flow does not require further application involvementonce the connection has been made. For example, data can be streamedfrom a camera through a camera logical device, across a channel, anddisplayed by a window logical device. The application can control thetwo logical devices via there signal ports; when the transmission is nolonger required, the application can disconnect the ports, close thedevices and remove the channel.

Device ports cannot be welded to channel ports, since this would allow adevice to exist outside the control of a local application. Logicaldevices are permitted to issue API calls to the support system, and inthis regard act on behalf of the owning application (ie the applicationwhich opened the device). Devices for example can cause their owningapplication to share with other applications, create channels, and sendor receive data.

Potential devices include:

    ______________________________________                                        system clipboard      LPTx                                                    DDE                   window                                                  shared clipboard      printer                                                 serial emulator       file                                                    video                 codec                                                   audio                 telephone                                               ______________________________________                                    

Shared use of the clipboard is facilitated by the system clipboard andthe shared clipboard devices. The system clipboard device may be openedby an application to provide a sending and a receiving port, givingaccess to the windowing system clipboard data at that node. Only onesending port may exist at any time, but any application at that node mayopen receiving ports. Through the use of channels, system clipboard datafrom one node, can be simply routed across to other members of anapplication sharing set.

Another device, the shared clipboard, is provided to ease data sharing.It is unique to a sharing set; only one sending port is allowed butmultiple receiving ports are supported. Apart from these distinctions,it behaves in a similar manner to the system clipboard and provides asimple mechanism for applications to share common data.

The window device, allows a window, defined on the screen, to beassociated with a sending or a receiving port (or in some circumstancesboth). The sending port can be connected to a channel port and data canbe streamed to the window and displayed. A variety of data formats aresupported.

The DDE device can be opened to provide sending and receiving portswhich are coupled to the dynamic data exchange mechanism. Through thisdevice an aware application can control an application that supportsDDE, or be itself controlled. Moreover, by establishing the appropriatechannels, two remote DDE applications can be linked together.

The printer device, allows data to be sent to the system printer; only asingle sending port is permitted.

The asynchronous serial device supports one sending port and multiplereceiving ports and interfaces to RS232, RS422 and other serialcommunications.

A number of video and audio devices exist including: the video displayand playback devices (supporting IBM/Intel ActionMedia II Adapter/A);the video capture device (supporting IBM M-Video Capture Adapter/A); theaudio capture and playback devices (supporting IBM M-Audio Capture andPlayback Adapter/A); and other specialised audio/video devices (such asH320 compliant codecs).

A number of aware applications are shipped as system utilities, and takeadvantage of these devices to offer general purpose end user functions,for collaborative working over a network.

Customisation

Customisation information for the support: system 17 is stored in anappropriate platform-designated repository; for Windows and OS/2 theseare the files called LAKES.INI and LAKESQOS.INI, formatted as a standardASCII file, containing sections headed by an identifier, where keywordsand their values are kept. Applications may also have their ownadditional initialisation filed. LAKES.INI contains standard sectionincluding information on configuration and start-up options, awareapplications, devices and physical communications link; additionallyapplication sections containing data specific to those applications maybe present. LAKEQOS.INI contains quality of service information relatingto physical links and data classes. Calls to access and update thesefiles are provided in the API.

Resource Management

Collaborative working frequently requires that resources owned by anode, for example a printer device, can be shared with other nodes. Suchresources are considered to be global resources and access is controlledthrough global tokens. Other resources are local to application sharingset, for example a shared pointer, and access to these is managedthrough application tokens.

A token owner determines the significance of a token and allocates it onrequest. At the discretion of the owner, queued requests may bepermitted, and more than one concurrent holder of a particular token maybe allowed. Token owners can optionally force holders to hand backtokens.

Global tokens share a common name space throughout the network, butsince applications are expected to know the location of a globallyavailable resource that they require, duplicate global token names arepermitted. Facilities for the broadcasting of availability informationare not provided; Instead, the call manager at the node with the globalresource is responsible for resource management and therefore holds anyglobal tokens. Global tokens may be held by an application instance onan exclusive or shared basis; token ownership, however, cannot betransferred to an application. Requests for a global token may bequeued, with the queue being held above the API and managed by the nodecall manager. Access to global tokens is not restricted to a sharingapplication set.

Application token name space is restricted to the application sharingset. Tokens may be owned by any member application and ownership can betransferred. Application tokens may be held on an exclusive or sharedbasis and requests for tokens queued, with the queue being held abovethe API, and managed by the current application token owner.

Initialisation and Termination

The support system is started by running a LAKES.EXE file, which readsthe profile data from the file LAKES.INI. The named call manager isstarted by the support system, which then registers itself as an awareapplication. A "set₋₋ call₋₋ manager" command then establishes thisparticular application as the call manager for that node. After thiscommand, the support system is fully active at that node and is able toprocess incoming events and requests.

Aware applications can be initiated, either by the usual operatingsystem procedures, such as a double click on an icon, or by a "launch"command. In the former case, the application will register with thesupport system, and in the return data receive its application and nodehandles. The call manager is notified of this registration, and supplieda handle to the application. In the latter case, the launchingapplication is returned a handle to the application; this is only validin very restricted circumstances until the launched application hasregistered with the support system. The return data provides thelaunched application with its application and node handles. Both thecall manager and the application that specified the launch (ifdifferent) are notified accordingly.

Applications may revert to unaware application status by de-registering,the call manager being notified. All tokens held are released and thetoken owners are notified; all tokens owned become invalid. If theapplication is a member of an application sharing set it is removed andthe other members notified of its departure. All ports created by theapplication are destoyed and the other applications owning ports to theaffected channels are notified. All channels connected by theterminating application are welded and appropriate events raised at theend channel ports. Appropriate events are raised is necessary to thelocal call manager, plus the call managers of any nodes supporting awelded channel on behalf of the deregistering application. All openlogical devices are closed; if any of the logical devices are connectedto ports, destroyed as part of the de-registration process, then thewhole connected channel is destroyed and the appropriate events raised.

A shutdown request can be issued by an application to close down thesupport system at a node in an orderly manner. This raises an event inthe local call manager, and if the call manager accepts the request,corresponding shutdown events are raised at the other' applications.These then prepare to close down and de-register, each de-registrationbeing notified to the call manager. After the call manager has beennotified that all the applications have de-registered, it toode-registers, to complete the shutdown.

The normal operation of the support system depends on the presence ofthe call manager. It is possible to replace the existing call managerwith another, but the existing call manager may reject the request to doso.

Applications may join other applications in a sharing set by issuing the"share₋₋ app" request and naming an application sharing set; the normalcase being where the target application and node are both specified byname. If an application at one node wants to share, by name, with analready existing instance of an application at another node, then theprocedure is as follows. App 1 at node 1 issues the "share₋₋ app"request, specifying its own applciation and node handles as tile source,and the names of app 2 and node 2 as the target. After verification withtile call manager at node 1, an appropriate request is sent by thesupport system to the call manager at node 2. Providing this callmanager accepts the request, this is then passed onto app 2, which canreturn a confirmation, assuming that it wishes to accept the share. Thisscheme provides for considerable flexibility in application sharing.Each call manager is aware of the share activity at its node, whetherapplications are the source or target of "share₋₋ app" requests.

A call manager has the following options on receipt of a share request:(i) handle the share itself (ii) transfer the share request (iii) rejectthe share (iv) launch a new application to handle the share (v) changethe application and node name.

An application is not a member of an application sharing set whenlaunched. When the source application issues a "share₋₋ app" request ithas the option of naming the resulting sharing set; if it does not namethe sharing set then the target must supply the name. After the share,both the target and the source join a new sharing set with this name. Ifeither the source and/or the target were already members of a sharingset with this same name, then those sharing sets are merged with thenewly created sharing set. Applications can leave a sharing set usingthe "unshare₋₋ app" request.

Data transmission and receipt

There are four mechanisms for applications to exchange data:

(i) User information strings

This is effectively a string passed to the support system as a parameterin an API call, which is then passed to the target application.

(ii) Signal function calls

These commands allow control information to be sent betweenapplications, and are not restricted to those applications within asingle application sharing set. Depending on the API call used, a replywill or will not be provided. Note that since this method uses thecommunications paths established between support systems on differentnodes for their own data control flows, this technique is restricted tolight data traffic.

(iii) Channel transmission

Channels are intended to support the transfer of volume data betweenapplications. They provide the only means of controlling the transportcharacteristics. The use of channels is restricted to applicationswithin the same application sharing set. When requesting the creation ofa channel, the following information is specified: target applicationhandle, channel set type and identifier, data class, maximum buffersize, user exit, node handle, quality of service, connect type, portevent handler, user information. An alternative approach to channelcreation is to take advantage of the channels created when applicationswith existing merged or serialised channel set are involved inapplication sharing.

Data is sent over channels by applications in packets; at the physicallevel the unit of data transmission is a frame. Certain data isspoilable, ie under certain conditions, if it cannot be delivered intime to meet the quality of service requirements, then it may bediscarded. Some packets can be marked as spoilable, other packets asspoilers. A spoiler packet, if present, will cause the removal of thosespoilable packets with which it has been associated. This techniquesupports for example the implementation of buffer management schemes forvideo, where certain pacekts are delta frame packets, and others arefull frame packets. Selected sequences of delta frame packets can andmust be deleted if a full frame is available.

(iv) logical devices

In certain specialised situations it is appropriate to use logicaldevices to exchange data. A single logical device can present ports tomultiple applications; the logical device can then move data between theports. This transport mechanism is not restricted to applications withinthe same sharing set and therefore overcomes a limitation placed onchannels; however logical devices cannot span across nodes. Moreover anynecessary quality of service support must be explicitly provided for bythe particular logical device.

Negotiation of Quality of Service

Applications lave different needs for quality of sevice and bandwidthnegotiation and control. For examples, the following may be required:

pre-determined and constant quality of service, eg G.711 voice

flexible requirements at channel creation, but constant thereafter, egfile transfer

single application management of channel resources, eg an applicationcommunicating multiple data types such as video, voice, and data underrestricted bandwidth conditions i.e. the video quality must be degradedintermittently to allow data traffic

cross application management of channel resource, eg a group ofapplications communicating multiple data types under restrictedbandwidth conditions and coordinating their activities as the prioritieschange for different types of data traffic

Certain applications have fixed quality of set-vice requirements for thechannels needed to communicate with other applications. In these casesthe channels may be established directly, using a "create₋₋ channel"request. Parameters on this request identify the receivingapplication(s) and both the channel and the sending portcharacteristics. If the resources are available, and the receivingapplications accept the request, then the channel will be created.

Some applications are more flexible in their quality of servicerequirements and need to determine what is available to a particularnode and then use this information in setting the parameters of the"create₋₋ channel" request. This is accomplished through a "query₋₋resource" command, specifying the target node. The subsequent "create₋₋channel" can request an equal or lower quality of service and expect therequest to be satisfied, if there is not competition for thecommunications resource.

Other applications have flexible quality of service requirements, butneed to compromise the specification over a number of channels. Thisrequires the application to reserve resources and then allocate fromthis reserved pool.

This is achieved by means of a "claim₋₋ resource" command specifying aresource set identifier, a quality of service, and the target node. Thishas the effect of reserving that resource and associating it with thespecified identifier. This identifier can then be specified in asubsequent "create₋₋ channel" command, in which case the resources areallocated from those reserves. The "query₋₋ resource" command can beused to determine remaining resources in a resource set.

Certain applications need to dynamically change their channelcharacteristics during execution; for example, available bandwidth mustbe re-allocated across channels. This can be done through a "change₋₋channel" request, specifying a resource set identifier. The resourcesare given to, or taken from, those resources associated with thatidentifier. This technique allows, for example, a fixed resource to besecured for an application to application communication, and thenre-allocated dynamically according to the traffic e.g. video bandwidthcan be temporarily reduced to allow faster file transfer.

Resource set identifiers are local to an application instance andcontain resources appropriate to one particular quality of service.

Networks

An application can specify quality of service characteristics whencreating a channel or when reserving resource for later allocation tochannels. Channels are mapped onto physical links; the data pacekts sentby applications over logical channels being implemented as data framessent over links.

Links are characterised by order, whether switched or fixed, theirtime-out parameters and by their quality of service characteristics.Order determines the order in which the support system will attempt touse the links for data transmission, assuming that there is a choice oflinks available with suitable data transmission characteristics. Order,switched or fixed link, and time-out parameters are specified in theinitialisation files.

Link descriptions, optionally including quality of servicecharacteristics, are stored in a link data base external to the supportsystem. Defaults for the quality of service information are contained inthe initialisation files. The data base is accessed by an installationsupplied executable, which is called by the support program. The qualityof service parameters relevant to digital links are: throughput,latency, jitter, frame size, frame error rate, frame re-transmissiontime, compression hints, encryption.

The key parameters used to characterise the quality of service requiredby applications over logical channels are: throgput, latency, jitter,packet size, packert error rate, encryption, compression hints,priority. Most of these mirror their link counterparts with theexception of channel priority, which specifies the order in which thesupport system will attempt to service data tranmissions over all thechannels at that node, assuming that there is resource contentionbetween the channels, and packet error rate, which specifies anacceptable random proportion of packets that need not be delivered dueto loss or error in transmission (there is no guaranteee that thesupport system will conform to such a limitation; specifying zero hereresults in the application being notified of any failures).

The above information is used to determine what links to use forapplication to application communication. A data base containinginformation such as type of link and service characteristics can beaccessed via the resources interface, whilst the channel information isobtained from the application. The support system then selects anappropriate link to use based upon matching the fully resolved channelrequirements with the fully resolved available links information, takingaccount of (a) the need to exchange control information between thesupport systems at different nodes, and (b) the order values associatedwith the links.

Both software and hardware compression and encryption are supported.Hardware features on a physical link are accommodated by considering thevarious combination of options as different available links types, eachassociated with particular transport characteristics. Software routinescan also be used, but these will not be invoked if specific latency andjitter requirements have been set.

In order that the complex process of route selection can be performedoutside the support system if necessary, the RLI calls used to retrievelink information also supply all the required channel quality of servicecharacteristics. Through this mechanism, an external routine can itselfdetermine the appropriate route and return that route to the supportsystem. An example of the need for this might be that transmission costsvary with the time of day.

When applications with channels share with each other, if their existingchannels belong to the same named merged or serialized channel set, thesupport systems create additional channels. An attempt is made toestablish these new channels from each sending port, with a quality ofservice appropriate to that port, ie an implicitly created channel willattempt to have characteristics such that it can transportsatisfactorily any data packets expected to be sent down any one of thepre-existing channels from that port. In some cases, due to restrictionsimposed by the capabilities of the available physical links, it will notbe possible to create channels with such characteristics. However, inall cases a channel will be created, and it is the responsibility of theapplication program to query the channel capabilities, if these arelikely to be significant.

A channel between nodes may be realised over a single physical link, orover multiple, serially connected links. The physical connectionexisting between two nodes is termed a route.

a) Permanent Digital Networks

The support system operates with either dedicated of shared, switched orpermanent, digital links between nodes. Shared links have unpredictablelatency and bandwidth characteristics, unless bandwidth managementfacilities are being employed. Such features give permanent links manyof the characteristics of switched connections.

b) Permanent Analogue Networks

The support system supports analogue communications in a very similarway to digital communications, in those situations where:

analogue links exist between nodes.

connectivity and routing at each node can be controlled by the system atthat node.

a digital control channel exists between the nodes.

Analogue channels are logically dedicated uni-directional communicationlinks established by the sending application, and they may terminate inmore than one receiving application. They may be distinguished fromdigital channels by their quality of service characteristics. Portsterminating these analogue channels have a null connect type since theycannot supply or receive data from applications. Only standard or mergedchannels may be established; serialsing and synchronising channel setsare not permitted.

Logical devices can present analogue ports when opened; thus a videoplayer device can be used as a source of analogue video and may beconnected to an analogue channel through an API command. The directconnection of analogue and digital channels is not permitted; howevercertain devices e.g. a codec device provide both analogue and digitalports when opened and can be used to effect such a coupling.

c) Switched Digital Networks

Switched digital networks can be used by the support system forinter-node communication without exposing the switched nature of theconnection. Information accessed via the resources interface is used bythe system to decide when to terminate an inactive switched connection.

Equipment, such as digital telephones, attached to a switched network,are accessed by applications in one of two ways. If a simple connectionis all that is required then the telephone may be regarded as a virtualphone application executing at a virtual node. The connection to thephone is initiated by a share request specifying the virtual phone asthe target, resulting in a telephone call established between atelephone associated with the local node and a remote telephone.Incoming telephone calls can be handled in the same way, ie as a sharerequest.

Alternatively, the phone may be accessed as a logical device. Thus anISDN phone device may be opened to present receiving and sending ports,with an associated event or command connect type: dialling, and othercontrol functions, are implemented through "signal.sub. port" commands.Third party connection between digital telephone equipment is similarlyaffected through commands to an appropriate device; this may bephysically implemented through commands to the local switch.

Potentially active multi-point control units, which dynamically modifydata or routing, for example, an MCU implementing the CCITTrecommendations for audio-visual communication, may also appear asdevices to applications.

d) Switched Analogue Networks

Analogue telephones and other equipment, attached to the public switchednetwork, may be accessed in a similar manner to digital telephones, eceither as a virtual phone application executing at a virtual node, orthrough a logical device. A PSTN telephone logical device can be openedto present a port, with a null connect type i.e. it cannot supply orreceive data from an application. "Signal₋₋ port" commands are used tocontrol the device. First party connection can be implemented through amodem injecting dialling tones into the local line; third partyconnection, and multi-way calls through commands to the local switch.

Interfacing to Unaware Applications

The support system provides facilities which permit unaware applicationsto be used for collaborative working. An aware application supplies theuser interface dialogue and interacts with the particular unawareapplication via virtual devices. This same aware application thencommunicates with a related aware application at the remote node to passthe information to the remote user. Several such applications areincluded as general purpose utilities.

A common requirement is for an application window of an unawareapplication to be displayed at a remote node as illustrated in FIG. 11.The implementation is as follows: an aware application A_(X) at node Xdialogues with the user to identify the window required, assumed here tobe the unaware application U_(X). A_(X) then opens a window displaylogical device, with the appropriate parameters, the effect of which isto generate a port through which copies of the window data are madeavailable. A_(X) connects this to a port on a channel leading to anaware application A_(Y) at the destination node Y. A_(Y) then opens areal window logical device, and connects the port created to thereceiving channel port. Data flows between the nodes, and is displayedat Y, without the further intervention of either application A_(X) orA_(Y). Options available on the windows logical device open requestallow the application to specify such parameters as bits/pixel,frequency of update and data format (e.g. text, bit map and option ofincluded pointer position).

Remote pointers over the shared window of the unaware application U_(X)can be handled by A_(X) and A_(Y) setting up a channel suitable for theinteractive data class. The real pointer on each node is then used foridentifying features in the shared window; this can be achieved with analgorithm such as: each user wishing to point moves his pointer into theshared window; when pointers are in the shared window their co-ordinatesare transmitted to the sharing applications. The combined co-ordinatesare then used to control the pointers; the effect is that whoever movesthe cursor last, positions all the linked pointers.

Remote printing and remote file generating are similarly accomplishedthrough logical devices. In the case of printing, a printer emulatordevice is installed at the source node. When it is selected as theprinter device by the user, the effect is to redirect the printer datastream to a port. This is then connected, via the aware applications, toa real printer device at the destination node. This general technique isextended for a range of other capabilities such as dynamic data exchange(DDE) and the system clipboard.

Remote control of an application or system is not supported directly;however an application to perform remote control can be implementedabove the API, with Lakes providing the group communication andmulti-media data transmission facilities.

Programming Considerations

a) Program Call Types and Structure

Program calls to the API generally result in a request, indication,response, confirm sequence. An application A, requiring a service,requests that service, supplying the appropriate parameters. The requestusually requires another application B being made aware of that request;the mechanism for this is an unsolicited event which appears as anindication at the application B. The action taken by B to the indicationevent is given to the support system as a response, with appropriatedata. The system passes the information back to application A as aconfirm event. This is illustrated in FIG. 12 using the example of thesequence involved in adding a port to a channel (for simplicity noparameters are shown).

An API call may be either synchronous or asynchronous, depending uponthe particular function; a synchronous call returns control when therequest is complete, an asynchronous call returns control immediately.To help applications monitor the progress of an asynchronous call, thesecalls contain a reference identifier. This identifier is valid until therequest has been satisfied and queries can be issued to obtain status;this same identifier can also be used to cancel a pending request. Allcalls pass back a return code denoting call status.

b) Addressability

An application requests addressability to nodes by using the node name.This name is first passed to the locak call manager which has the optionto modify it. The resultant name is then used by the support system todetermine connectivity information, this requires access to theexternally held network and user data base, using the resourcesinterface. Thus the support system determines physical addressabilityfor that name through queries to the network configuration via theresources interface 29, FIG. 2. A node handle is returned to theapplication to reflect this resolution of the node name. Addressabilityfrom one application to another application requires the resolution ofan application name. If both applications are at the same node, thelocal call manager can perform this resolution, else both call managersmust be involved. This resolution results in the target applicationbeing identified to the source application by an application handle.Calls using application names are always passed to the call manager forresolution; calls using application handles go direct to the specifiedapplication.

When an application creates a channel, addressability to the channelport is provided through the system returning a port handle. Similarlythe opening of a logical device results in a device port handle.

All handles are guaranteed to be unique to the using application but arenot valid if passed to other applications or nodes.

c) Event Classes and Event Handlers

API requests are provided to assist with event and call control. A"begin₋₋ monitor" request allows an application to monitor requests andevents at a node, the scope of the monitoring being controlled by thechoice of monitor class from one of the following:

All: all events or API calls

Application Signalling: signal events/API calls

Call₋₋ manager: call manager events/API calls.

Data: data transmission events/API calls.

Device: device events/API calls.

Monitor: monitor events/API calls.

Port: port and channel events/API calls.

Profile: profile events/API calls.

Share: share and unshare events/API calls.

Synchronisation: synchronisation events/API calls.

Token: token events/API calls.

The scope of the monitoring is controlled at the event or API classlevel. Events can be monitored with or without data. Monitoring isterminated with an "end₋₋ monitor" command. Applications can also usethe "enable₋₋ events" and "disable₋₋ events" commands to determine whichevents they are to receive. The valid event classes are:

All: all events

Device: device events

Port: port and channel events

Profile: profile events or API calls

Sharing: share request events or AFI calls

A default event handler generates responses for all events notexplicitly handled via an applications. Events are handled by registeredevent handles: four types can exist in aware applications:

Application: this is the primary event handler thant handles the mainevents related to the general operation of an aware application. Thisevent handler must be present in all aware applications, including acall manager.

Call₋₋ manager: this is somewhat specialised and handles those eventsconcerned with application registration, name resolution, shutdownrequests, passive nodes, call manager transfer, and global token status.This event handler must be present in all call managers.

Port₋₋ event handler: more than one port event handler may be presentand each handles data communications related events.

Monitor: this is optionally present and handles all monitoring ofevents.

d) Other Programming Facilities

All channel ports can be associated with a user exit to monitor datatraffic or process data. For a sending port, the user exit is invokedimmediately prior to the data being transmitted to the receiving nodes;for a receiving port, the user exit is invoked immediately the dataarrives at the receiving port but prior to the data being presented tothe receiving application. Specification of a user exit routine on portswhich have been connected may impact performance because the data mustbe surfaced to the user exit.

A full set of queries are provided to avoid applications needing to keeptrack of status information.

Application program debugging can be simplified by initially runningcollaborating applications at a single node; this avoiding physicalnetworks being required during initial stages of program development.

No user interface code exists below the API; all user interactions arethe responsibility of either the application program, or the codeservicing requests across the resources interface.

Utilities

A number of pre-programmed utilities are provided in order toimmediately provide useful function to end users and reduce theprogramming effort required to develop new collaborative applications,by providing common functions accessible through a command interface.

All the utilities are replaceable application programs. The structure ofthe provided utilities is shown below in FIG. 13. The supplied utilitiesinstall as a program group and are designed as a suite of applicationswhich work together. The major utility functions can be invoked fromother application programs by means of the "signal" command, as well asdirectly by the user.

a) Directory and Call Management

i) Address Book

The address book utility 100 allows an end user to add, delete andupdate directory and connectivity information. The data is stored in asimple file structure which is easily edited by standard programs,although a mechanism is provided to interface with other potentiallymore extensive and complex address data-bases. User data can be groupedinto logical collections known as phone books. The utility interfacesdirectly to the call manager; it also responds to queries through theresources interface.

ii) Call Manager

The call manager utility 101 implements the concept of a call. A callrefers to a group of users collaborating by using shared applications.More than one call can exist at any time, users can be in more than onesimultaneous call, and the same applications can be executed in multiplecalls. For example: the users A, B and C can be in a call, x, to reviewa document; all may using voice communication with each other, A and Bmay also have a video link, and A and C may also have a sharedchalkboard. Meanwhile, A, B and D may be in a second call y, to review asecond document; with A and D using a chalkboard, and B and D usingvoice links.

The call concept does not exist in the API but it is implemented by thecall manager through application sharing sets. Providing this supportavoids the need for aware applications to be involved in call set-up ortear-down and provides clear separation of call management andapplication programming. The call manager provides dialogues for an enduser to select names from the address book and logically establish amulti-point call. Parties can be added and deleted dynamically. Optionsprovided include auto-answer and call barring. One call is deemed to bethe current active call and it is the one to which shared applicationsare normally added when invoked. The current active call may berelegated to the background whilst another call is set-up.

b) User Utilities

i) Application Assistant

This utility implements the following functions for users in a call:

direct mirroring of an existing application window, either as a snapshotor continuously, and has the system pointing device enabled as a remotepointer.

system clipboard support i.e. the ability for the contents of a systemclipboard at one node to be optionally shared and/or viewed at othernodes.

remote DDE links able to be established between applications atdifferent nodes.

redirection of printing to printers at other nodes.

ii) Chalkboard

The chalkboard 103 implements a common drawing area with two imageplanes, which is accessible to all users in a call. The background planecan be loaded from bit-map files, the system clipboard, or from thecontents of an application window. The foreground plane can be used forinteractive annotation using a range of simple text and graphics tools.Remote pointers over the chalkboard are also supported.

iii) File Transfer

File transfer 104 allows the transmission of files between users in acall. One or more ,files can be transferred, the files can be sent withcomments, and the original file names are made available to thedestination. The receiving node is in full control of file receipt andfile naming.

iv Message

Message line 105 provides immediate sharing of text data between usersin a call. Multiple simultaneous users are permitted; each participantsees all the exchanged messages, and in the same sequence. The messageutility also logs activity during the call; such as calls set-up andterminated, and files transferred, In an actual embodiment this utilityis provided as part of the call manager.

v) Video/Voice Link

This utility 106 allows the establishment of video and voice linksbetween users in a call. The precise function available is dependentupon the capabilities of the physical network and the workstationhardware support.

Standards

The overall architecture is intended to support a broad range ofcollaborative applications. The interface is set at as high a level aspossible, consistent with not imposing any significant restraints on therange of application models that may be implemented. The nature of thetransport networks involved are totally hidden below the API. This meansthat an application is completely unaware of the network routing (egdirect or indirect), and the network types involved (eg single ormultiple links, switched or fixed connections). A consequence of thisapproach is that the applications must be written expecting thatrequests, for example for a particular communications quality ofservice, may fail, since the underlying network may not have therequired capability.

An agent philosophy has been implemented so that third partyapplications can be sued to act on behalf of other applications. Thispermits call manager, telephony, and switching applications to bedeveloped. The current state of technology requries that analog networksand devices should be supported. It is attempted to treat analognetworks like digital networks, in order to ease application migration.

At the API level, one of the key concepts exposed is that ofapplications sharing sets. Applications are expected to collaborate withother applications, and the mechanism for this colloboration is thatthey join each other in named application sharing sets. The essence ofsuch an application sharing set is that all set members receiveinformation on the status of all the other members; joining a set is theway in which applications declare those in which they have an interest.The concept of the call by contrast exists above the API, and inparticular at the call manager. It is possible for different callmanagers to have different call models.

Alongside the application sharing set, the channel is the otherfundamental concept in the architecture. Uni-directional channels areused as the basic communications building block to efficiently supportboth broadcast and two-way communications. The channels are establishedby the sending application, and accepted by the receiving application,because only the sending application can be aware of the properties ofthe data which dictate how it should be transmitted. Both applicationscan independently control the format to be supplied or received to orfrom their respective ports. Multiple logical channels, for each kind ofdata flow, allow the support system to allocate the trafficappropriately to the underlying transport network; moreover it letsother applications have data presented to them in separated, homogeneousflows, each individually described. Additionally this split of theinter-application traffic into individual data types, allow the supportsystem to offer data conversion facilities.

Connections and welding of channels allows the transport of data to dropbelow the API so that the application is no longer involved in movingthe data. The support system has the option, in some cases, of effectingthe connection, either at a very low level at that node, or re-routingthe flow away from that node.

The support system architecture is designed to permit inter-workingbetween different computer platforms, operate over varied communicationsnetworks, and support relevant communication and data standards.

The separation of data traffic into logical uni-directional flows ofhomogeneous data, simplifies the mapping on to a mixed network andallows the use of multiple physical links, of different capabilities,between the nodes. Data multiplexing is handled below the applicationand can be implemented in different ways depending upon the underlyingtransport mechanism, e.g. by a combination of: allocating each logicalflow to an individual physical link; multiplexing all the data in thesupport layer; or by leaving aspects of the multiplexing to a devicedriver. Through this means voice, video and data traffic, for instance,can be sent over multiple channels, over iso-LAN or iso-Ethernet, orover ISDN using the CCITT H320 recommendations. The quality of servicerequirements impose conditions on the required transport facilities:thus voice and video typically require dedicated physical links orshared links with isochronous capability, implemented through schemesinvolving priority and bandwidth management.

The separate logical data paths provided by channels, with theirassociated data types, ease inter-application operation because the datacomponents are presented individually, with their nature and formatindependently available. Through this mechanism, a wide range ofexisting standards for voice, video, image, file transfer, and codeddata can be supported, with the potential for the support system toperform data conversions in the network. The system also provides aseparate data class for the interactive objects commonly used incollaborative applications, such as remote pointers, cursors andgestures.

Overview of the API Commands

The principal facilities offered by the API calls are detailed below.The syntax and parameters of the actual calls is not described becausethe intent is only to give an overview of the scope.

API Function Requests

Session and application sharing

cancel₋₋ request: cancels a previous asynchronous request if thatrequest is not already satisfied.

deregister₋₋ app: issued by an application instance to terminate its useof the API.

launch₋₋ app: issued by an application to invoke another application.

register₋₋ app: identifies the issuing application instance as a wireand establishes the application event handler.

set₋₋ call₋₋ manager: identifies the call manager for that node andestablishes tile call manager event handler.

share₋₋ app: issued by an application instance to request the sharing ofone application with another application.

shutdown₋₋ node: issued by an application instance to request theshutting down of the support system at its local node.

unshare₋₋ app: issued by an application instance to terminate thesharing of one application instance with another application.

Devices and Ports

add₋₋ channel: adds, in a specified application instance, anotherchannel to a specified sending port.

change₋₋ channel: changes the specified channel characteristics.

change₋₋ device₋₋ characteristics: changes the specified devicecharacteristics.

change₋₋ port: changes the specified port characteristics.

claim₋₋ resource: call to a resource manager for resources associatedwith a particular quality of service.

close₋₋ device₋₋ port: closes the associated port on the defined device.

connect₋₋ ports: connects a specified receiving port to a specifiedsending port.

create₋₋ channel: creates a data transmission channel consisting of asending port at the issuing application and a receiving port at thespecified target application.

disconnect₋₋ ports: disconnects the specified receiving port from thespecified sending port.

open₋₋ device₋₋ port: opens a port on a defined device.

remove₋₋ channel: removes the channel associated with the specifiedreceiving port and the specified sending port.

request₋₋ resource: enquiry to a resource manager for resourcesassociated with a particular quality of service.

resume₋₋ port: resumes data transmission through the specified port.

signal₋₋ port: transmits a control string through a specified port.

suspend₋₋ port: suspends data transmission through the specified portafter draining or flushing any data not yet received.

weld₋₋ connection: makes the connection of the specified receiving portand the sending port permanent.

Data Transmission and Receipt

receive₋₋ data: receives data from the specified receiving command port.

send₋₋ data: sends data asynchronously through the specified sendingport. Various transmission acknowledgements may be requested.

signal: transmits support system or application defined control dataover a support system established control channel to a specifiedapplication instance.

signal₋₋ app₋₋ with₋₋ reply: transmits support system or applicationdefined control data over a support system established control channelto a specified application instance, and returns the response data.

start₋₋ sync: starts the synchronisation of data received throughreceiving ports associated with a specified channel set.

stop₋₋ sync: stops the synchronisation of data for all receiving portsassociated with a specified channel set.

Token Management

get₋₋ token: requests the immediate holding of the specified global orapplication token either exclusively or in a shared manner.

give₋₋ token: gives the specified token to the specified requester.

qget₋₋ token: requests either the holding of the specified global orapplication token either exclusively or in a shared manner, or, if thetoken is not available, the joining of a request queue maintained by thecurrent owner.

reclaim₋₋ tokens: forces the specified token held by the specifiedapplication instance to be immediately released back to the currentowner of the token.

refuse₋₋ token: refuses the specified token to the specified requester.

release₋₋ token: releases the specified held token back to the currentowner.

return₋₋ token: requests that the specified application instance holdingthe specified token should return the token back to the current owner assoon as possible.

set₋₋ token₋₋ owner: sets the owner of the specified token to thespecified application instance.

Event Control

begin₋₋ monitor: causes special monitoring events identifying eachoccurrence of an API call, and/or a normal event to be presented to thespecified monitoring event handler,

default₋₋ event₋₋ handler: returns default responses for all events thatan application programme does not wish to handle explicitly.

disable₋₋ events: stops events of the specified event class being passedto the event handler of the issuing application instance.

enable₋₋ events: allows events of the specified event class to be passedto the event handler of the issuing application instance.

end₋₋ monitor: stops the special monitoring events identifying eachoccurrence of an API call, and/or a normal event being presented.

Profile Management

read₋₋ profile₋₋ string: returns a character string of a specifiedkeyword in a specified section from a profile file.

write₋₋ profile₋₋ string: copies a character string to a specifiedkeyword in a specified section the profile file.

API Queries

query₋₋ address: returns the completed full address of an applicationinstances belonging to a named sharing set.

query₋₋ application₋₋ status: returns status of an application (unaware,aware or call manager).

query₋₋ channel₋₋ characteristics: returns the channel characteristicsof the channel associated with the specified sending and receivingports.

query₋₋ channel₋₋ set: returns the handles of all the ports in aspecified channel set.

query₋₋ device₋₋ characteristics: returns the device characteristics ofthe specified device.

query₋₋ device₋₋ status: returns the status of the specified device.

query₋₋ monitor: returns the class of functions or events currentlybeing passed to the monitor event handler.

query₋₋ port₋₋ characteristics: returns the characteristics of thespecified port.

query₋₋ port₋₋ status: returns the status of the specified port.

query₋₋ resource: returns the resources available in the specifiedresource set,

query₋₋ sharing₋₋ set: returns the sharing set identifiers for anapplication instance,

query₋₋ token₋₋ holder: returns the owner (application tokens only) andholder of a token,

query₋₋ token₋₋ state: returns the state of the specified token,

API Events

Call Manager Events

APP₋₋ DEREGISTERED: an event to the local call manager when theapplication instance terminates its use of the API,

APP-REGISTERED: an event to tile local call manager when an applilcationinitializes its use of the API,

CALL₋₋ MANAGER₋₋ ERROR: an error has occurred which affects the callmanager,

CALL₋₋ MANAGER₋₋ REQUEST: an event to the local call manager indicatingthat another local application has issued a set₋₋ call₋₋ managerfunction request,

NODE₋₋ SHUTDOWN₋₋ REQUEST: a request for the support system to shutdown.

PASSIVE₋₋ NODE₋₋ RELEASED: an indication that the resources allocated toallow the node to support passive requests may be released,

PASSIVE₋₋ NODE₋₋ REQUEST: a request for the node to allocate resourcesto support a passive request,

SHARE₋₋ REQUEST: a request to share with a named application,

TOKEN₋₋ STATUS₋₋ REQUEST: a request for status of a global token,

Application Events

APP₋₋ SIGNAL: a signal has been received.

APP₋₋ SIGNAL₋₋ REJECTED: a signal has been rejected.

APP₋₋ SIGNAL₋₋ WITH₋₋ REPLY: a signal₋₋ with₋₋ reply has been received.

APP₋₋ SIGNAL₋₋ TRANSFERRED: a signal has been transferred.

APP₋₋ UNSHARE₋₋ REQUEST: a third party local application has requestedthat the recipient leave an application sharing set.

APP₋₋ UNSHARED: a notification the issuer is leaving an applicationsharing set has been received.

APP₋₋ ERROR: a related application error has been detected.

NODE₋₋ SHUTDOWN: a shut down has been initiated.

PORT₋₋ REMOVED: a confirmation that a port has been removed.

PORT₋₋ REQUEST: a request to add a receiving port.

RESOURCE CLAIM: raised whenever an application claims its quality ofservice resources.

RESOURCE REQUEST: raised whenever an application requests its quality ofservices resources.

PROFILE₋₋ CHANGED: an indication that the LAKES.INI or LAKESQOS.INI filehas been changed.

SHARE₋₋ CONFIRMED: a confirmation that a share request had processed hasbeen received.

SHARE₋₋ REJECTED: a request to share has been rejected.

SHARE₋₋ REQUEST: a request to share has been received.

SHARE₋₋ TRANSFERRED: a request to share has been transferred,

TOKEN₋₋ CANCEL₋₋ REQUEST: a request to cancel a queued token request basbeen received.

TOKEN₋₋ GIVEN: a token has been given to a requester.

TOKEN₋₋ QREQUEST: a request to hold a token or to join the queue if thetoken is unavailable.

TOKEN₋₋ RECLAIMED: a token has been taken away by owner.

TOKEN₋₋ RECLAIMED: a token has been taken away by owner.

TOKEN₋₋ REFUSED: a request for token has been refused.

TOKEN₋₋ REQUEST: a request to hold a token.

TOKEN₋₋ RETURN₋₋ REQUEST: the owner of the token requires that the tokenbe returned as soon as possible.

Device and Port Events

CHANNEL CHANGED: some channel characteristics have been changed.

CHANNEL₋₋ CONFIRMED: a new channel has been created.

CHANNEL₋₋ DESTROYED: a channel has been destroyed.

CHANNEL₋₋ REJECTED: a channel has not been created.

CONNECTION₋₋ WELDED: a wel connection notification has been received.

DATA₋₋ AVAILABLE: data is available at a receiving port.

DATA₋₋ CONFIRMED: a confirmation of a data transmission has beenreceived, or an estimate of the progress of a data transmission.

DATA₋₋ REQUESTED: data is requested from a sending port.

DEVICE INFORMATION: an event raised to the sending port event handler ofthe application instance that is to supply device information.

PORT₋₋ ERROR: a port: error has been detected.

PORT₋₋ RESUME₋₋ REQUEST: a resume port request has been received.

PORT₋₋ SIGNALLED: a signal port event has been received.

PORT₋₋ SUSPEND₋₋ REQUEST: a suspend port request has been received.

PORT₋₋ SYNC₋₋ REQUEST: a request to adjust the synchronising control hasbeen received,

Monitor Control Events

EVENT₋₋ MONITORED: a notification of function request and eventactivities has been received.

Channel₋₋ l₋₋, Port and Link Characteristics

Channel Characteristics

The following parameters are associated with a channel and areestablished on the creat₋₋ channel and add₋₋ channel requests.

quality₋₋ of₋₋ service:

signal type (analog or digital)

throughput

latency

jitter

lateness

priority

compression hints

encryption

Quality of service characteristics are associated through data type andsubtype in the LAKESQOS.INI file, but can be specified explicitly. Theymay be left undefined; this allows channels to be created whoseoperational characteristics depend upon the resources available whendata is being sent down the channel.

channel₋₋ type:

standard

merged

serialised

synchronised

channel₋₋ set₋₋ id:

identifier

Port Characteristics

The following parameters are associated with a port; all exceptport-type are defined explicitly; sending ports specify these parameterson the create₋₋ channel request, receiving ports specify them on thePORT₋₋ REQUEST response.

connect₋₋ type:

command

event

null

event₋₋ handler:

port₋₋ type:

sending

receiving

data₋₋ class:

data type

data sub-type

user₋₋ exit:

user₋ information

Link Characteristics

The following quality of service parameters are associated with aphysical link and are specified in the network data base accessed viathe link locator, or obtained as defaults from the LAKESQOS.INI file.

signal type (analog or digital)

throughput

latency

jitter

frame size

frame error rate

frame re-transmission time

compression hints

encryption

Support System Structure

Referring back to the support system structure as illustrated in FIG.10, the various tasks of the components thereof will now be described inmore detail. The application manager 223 acts as an interface to therest of the support system, providing an entry point for all the APIcalls which are then distributed to the appropriate component after acertain amount of parameter verification, It is also used to scanincoming calls/outgoing events if monitoring is required (see below).

The application manager is responsible for calling back the applicationat the event handler specified when a channel is created. The eventswill be those raised at the sending port if the local applicationcreated the channel, or then receiving port if the remote applicationcreated the channel. When creating a port, the application managerpasses the address of an event queue handler which will handle all theevents for a particular application and place them in a queue. Then,some mechanism such as a dispatch thread continuously reading the eventqueue sends the event to the application's event handler.

The channel manager 227 has five sub-components: a channel supervisor,responsible for starting and shutting down all the other components; acontrol channel sub-component, which handles control channelcommunications between support systems at different nodes; a datachannel sub-component, which handles all other non-control channel datacommunications; a node manager, which creates, destroys, and maintainsnode handles and sets of node handles; and a port manager, whichcreates, destroys, and manipulates ports and does port query functions.

The resource manager 225 is the first component in the support system toget control. It is responsible for initialising all the othercomponents, as well as interfacing to any address book or routeselection facilities. The token manager 224, as its name suggests, isresponsible for the logging and management of tokens, both global andapplication tokens (global tokens are owned by the respective callmanager components; by contrast application tokens are owned by a nodein a sharing set).

The device manager 224 is responsible for interactions between thesupport system and devices, and in particular performs the followingfunctions: resolving devices names to fully qualified path etc, loadingappropriate dynamic link library (DLL), generating a record containingthe port number, port handler and event word, calling the initialisationentry point, and resolving all entry handles in the DLL to physicaladdress for the application call manager. The signal manager 226 isresponsible for signalling to applications (with or without reply) andto ports.

Sharing and Call Manager Installation

Having now described the overall operation of the collaborative supportsystem, various sharing and call manager set up operations will now bedescribed in more detail. The API command which establishes a callmanager is set₋₋ call₋₋ manager.

The set₋₋ call₋₋ manager function requests that the issuer beestablished as the new call manager at the issuing node and identifiesthe event handler to be invoked for call manager events.

Parameters required by the set₋₋ call₋₋ manager functions are:

    ______________________________________                                        event.sub.-- handler                                                                       the event handler to be invoked for call                                      manager events.                                                  event.sub.-- word                                                                          A user specified data pointer passed to the                                   call manager event handler on all call                                        manager events.                                                  call.sub.-- manager.sub.-- info                                                            (returned). The value returned by the                                         current call manager in response to the                                       SET.sub.-- CALL.sub.-- MANAGER event.                            ______________________________________                                    

The set₋₋ call₋₋ manager() function identified to the subsystem theevent handler that is to receive any events of a non-applicationspecific nature, i.e. any incoming events from tile network that do notidentify a specific application instance. (Note. The events may specifya destination application name, in which case, it is the function of thecall manager to resolve the name to a specific instance).

Only one set₋₋ call₋₋ manager() event handler can be active at any onetime on any given node. More than one set₋₋ call₋₋ manager() may beissued by applications running on a given node, but the last one issuedis the one that is ill effect (i.e. that application instance is thecall manager for that node).

Before issuing the set₋₋ call₋₋ manager() function call an applicationmust have issued an register₋₋ app() function all to identify itself tothe local system.

When a new application issues a set₋₋ call₋₋ manager() function call,the processing depends on whether or not there is already an existingcall manager.

If no call manager exists then no event is raised and the issuer becomesthe current call manager.

If a call manager already exists then it will receive a SET₋₋CALL-MANAGER event. This existing call manager has the option ofallowing the transfer of the call manager function to the newapplication or rejecting the request. In this case the existing callmanager stays in control and the issuer receive the RC₋₋ CM₋₋ REQUEST₋₋REJECTED return code. This allows some control over which applicationsare authorised to become call managers.

There must always be an application instance running that has issued aset₋₋ call₋₋ manager, otherwise no communication can happen with anyother node.

The LAKES.INI file can have a section in it, specifying the names of theapplications that are authorised to become call managers. So that when aSET₋₋ CALL₋₋ MANAGER event is raised at the current call manger, it cancheck in the file via the get₋₋ profile₋₋ string function call to see ifthe application is authorised.

The register₋₋ app function registers the name of the issuingapplication instance and the event handler to handle incoming events.

Parameters required are:

    ______________________________________                                        application.sub.-- name                                                                    The name by which the issuing application                                     is to be known to the system                                     event.sub.-- handler                                                                       address of the event handler to be                                            invoked by the system to handle                                               incoming events for the issuing                                               application instance.                                            event.sub.-- word                                                                          A user specified data pointer passed to the                                   call manager event handler on all call                                        manager events                                                   node.sub.-- handle                                                                         (returned) node handle to issuing node                           application.sub.-- handle                                                                  (returned) application instance handle                                        to issuing application.                                          ______________________________________                                    

In order for an application instance to be allowed to communicate withthe system, it must identify itself by issuing an register₋₋ app call.This call must be issued prior to any other calls from this instance,otherwise the calls will fail and an error code returned.

The application₋₋ name,event₋₋ handler and the event₋₋ word must besupplied. The node₋₋ handle and application₋₋ handle are returned by thesystem. They define the unique handles within the node and have no scopeor meaning outside of the local node.

As a result of the register₋₋ app function call, an APP₋₋ REGISTER eventis raised in the call manager even handler if one exists. If no callmanager exists then no event is raised and the issuer of the register₋₋app function call will receive the return code RC₋₋ NO₋₋ CALL₋₋ MANAGER,The issuer should then either become the call manager by issuing theset₋₋ call₋₋ manager() function call or terminate by issuing thederegister₋₋ app() function call.

This is the only function call that is valid prior to a set₋₋ call₋₋manager() having been issued, i.e. prior to a valid call manager havingbeen identified.

The launch function causes the specified target application to beinvoked.

Parameters required are:

    ______________________________________                                        target.sub.-- application                                                                    pointer to a structure containing                                             the full address of the target                                                application. The full address                                                 structure type is defined as                                                  follows:                                                       target.sub.-- exe.sub.-- string                                                              pointer to a character string                                                 specifying the fully qualified                                                name (including the full path)                                                for the executable for the target                                             application.                                                   working.sub.-- directory                                                                     pointer to a character string                                                 specifying the directory. IF the                                              working.sub.-- directory is null then                                         the current directory is assumed.                              parameters     a user specified string that is given                                         to the launched application.                                   application.sub.-- handle                                                                    (returned) application instance                                               handle                                                                        of the launched application.                                   ______________________________________                                    

This function is used to ask the system to start another applicationinstance. IF the new application is started successfully then itsinstance handle is inserted in the target₋₋ application and returned tothe calling application.

It is up to the launched application to use an register₋₋ app to fullyidentify itself to the system (if it is to be an aware application).launch may be issued by any aware application, it is not restricted tothe currently active call manager.

The share function requests that the specified target application beshared with the specified source application.

Parameters required are:

    ______________________________________                                        async.sub.-- id                                                                            a user supplied reference id by which this                                    call and all events related to this call may                                  be identified. This parameter can not be                                      zero.                                                            source.sub.-- application                                                                  pointer to a structure containing the full                                    address of the source application.                               target.sub.-- application                                                                  pointer to a structure containing the full                                    address of the target application.                               user.sub.-- info                                                                           a user specified string that is returned on                                   all events generated by this share.                              ______________________________________                                    

Possible Return Codes are:

    ______________________________________                                        RC.sub.-- OK     Operation completed                                                           successfully.                                                RC.sub.-- FAIL   LAKES environment not                                                         established.                                                 RC.sub.-- SHARE.sub.-- CONFIRMED                                                               returned to a synchronous                                                     share( ) to confirm that                                                      the share has been accepted                                  RC.sub.-- SHARE.sub.-- REJECTED                                                                returned to a synchronous                                                     share( ) to confirm that                                                      the share has been rejected                                  RC.sub.-- INVALID.sub.-- ADDRESS                                                               Invalid address structure                                    ______________________________________                                    

The share function request that the source application and targetapplication are to be (or added into) an "application set".

If the target application is specified by name, then the call manager atthe relevant node will be invoked, it is then the responsibility of thecall manager at the target node to decide how to handle the sharerequest.

If the target application is specified by instance handle, then theshare request is passed directly to the desired application and does notgo via the call manager.

The user₋₋ info parameter would should normally be used to tell thetarget node how or why the application is to be shard.

The appropriate return code (RC₋₋ SHARE₋₋ CONFIRMED or RC₋₋ SHARE₋₋REJECTED) will be returned. If the local system receives a subsequentSHARE₋₋ CONFIRMED event from the target application then this event isnot raised to the issuer of the share function call but is handled bythe system generating an appropriate UNSHARE event, IF the local systemreceived a subsequent SHARE₋₋ REJECTED event from the target applicationthen this event is ignored.

A share request specifying an application name rather than a handle, isdirected to the call manger. This allows the call manager to decide howtreat the share, e.g. it could:

launch the specified application thus creating a new instance

launch a completely different application.

direct the share to an existing instance

redirect the share to a different instance

handle the share entirely within the call manager.

If the call manager issued a launch for an application as a result of aSHARE₋₋ REQUEST event, it must then re-issue the share request on behalfof the original requester to the launched application.

The unshare function terminates the sharing between the sourceapplication and the applications in it sharing set.

PARAMETERS required are:

    ______________________________________                                        async.sub.-- id                                                                            a user supplied reference id by which this                                    call and all events related to this call                                      may be identified. This parameter can not                                     be zero.                                                         source.sub.-- application                                                                  pointer to a structure containing the short                                   address of the source application. A short                                    address structure is defined as follows.                         user.sub.-- info                                                                           a user specified string that is returned to                                   all the application instances remaining in                                    the shared set on the events generated                                        by this unshare.                                                 ______________________________________                                    

This function is used to remove an application instance from a set ofsharing applications, it does not terminate the application. All otherapplications in the set will receive an event to indicate that theinstance is no longer part of the sharing set.

The user₋₋ info parameter- should be used to tell the other instances inthe application set why the unshare is being done.

Any ports owned by the instance will be dropped and events raised at theother end(s) of the logical channel(s).

The event handler set-up by the register₋₋ app is still active and willreceive events directed via the system or the call manager.

Typical flows for the control of sharing are illustrated in FIG. 14. Fora share in which only the name and not the handle of the targetapplication is specified then the SHARE₋₋ REQUEST event is raisedinitially in the call manager at the target node. For a share request inwhich the handle of the target application is specified the SHARE₋₋REQUEST event is raised directly in the target application.

At Step 1

Application X issues an asynchronous request to initiate sharing withapplication Y, Since the request specified only Y's character stringaddress the SHARE₋₋ REQUEST is raised to the call manager at Y's node,node 2.

At Step 2

Y's call manager has a number of options. It may reject the sharerequest (RC₋₋ SHARE₋₋ REJECTED), it may satisfy the share request itself(RC₋₋ SHARE₋₋ CONFIRMED), or it may decide to pass on the share requestto a new instance of application Y, (RC₋₋ SHARE₋₋ NO₋₋ CONFIRM).

At Step 3

If the call manager returns either RC₋₋ SHARE₋₋ REJECTED or RC₋₋SHARE-CONFIRMED then the subsystem will raise either a SHARE₋₋ REJECTEDevent, or a SHARE₋₋ CONFIRMED event at the requester.

At Step 4

If the call manager issues a launch function call specifying Y as thetarget application then a new instance of Y is started. The subsystemallocates an application handle for Y and returns it to the callmanager. It is assumed that after being started Y will want to becomeaware hence it will issue an register₋₋ app function call identifyingitself to the subsystem. The subsystem returns to Y the handle itallocated at launch.

At Step 5

As a result of the register₋₋ app the subsystem raises an APP₋₋REGISTERED event to node 2's call manager.

At Step 6

Node 2's call manager will then issue a share request on behalf of Xspecifying Y's handle and return with a RC₋₋ OK.

At Step 7

application Y will then receive a SHARE₋₋ REQUEST event identifying X asthe requester. Y may then either reject (RC₋₋ SHARE₋₋ REJECTED) oraccept (RC₋₋ SHARE₋₋ CONFIRMED) the share.

At Step 8

X will receive the appropriate SHARE₋₋ REJECTED or SHARE₋₋ CONFIRMEDevent.

At Step 9

if the share is accepted and X is also sharing with other applicationinstances then the subsystem at node 1 will send a SHARE₋₋ CONFIRMEDevent naming X as the source and Y as the target and also Y as the newsharer to all these applications. In turn, the subsystem at the nodeswhere these applications are running will send SHARE₋₋ CONFIRMED eventsto Y naming X as the source, Y as the target and themselves as the newsharer.

Finally at Step≢10

X may later issue an unshare() to leave the sharing set. All remainingapplications in the set will also receive an UNSHARE event.

The Call Manager plays a key role in determining the behaviour orpersonality of the subsystem at a workstation. The Call Manager utility101 (FIG. 13) supplied with the subsystem will now be described indetail.

The supplied call manager utility allows a clear separation of callmanagement and application programming. Use of tile shipped call managertherefore removes the need for aware applications to be involved in callset-up or tear-down. It provides dialogues for an end user to selectnames from the address book and logically establish a multi-point call.Parties can be added and can leave dynamically and several calls may bein progress simultaneously. Options provided include auto-answer andcall barring,

In order to separate the look and feel of the call manager from thefunction, the call manager is actually implemented as two separateprograms--the engine and the user interface. The engine provides callmanagement function, whilst the user interface determines tile look andfeel. The call manager engine has a command interface to all it to becontrolled by other applications (in fact this is how the user interfaceportion control the engine). The engine maintains an application table,for each local application instance currently running, a call table, foreach call, a command table for each application currently in the commandsharing set (and therefore eligible to send commands to the engine), anda link table, listing each passive link currently in effect.

The Supplied Call Manager Utility

The Call Manager lets the user initiate the following actions:

start a new call (note that a node may be engaged in several calls atthe same time, each with their own set of shared applications and otherparties)

add an existing unshared application to a call

unshare an existing application from a call

extend a call by adding a new person to it (if the callee accepts, anycurrent applications within the call will be shared with them)

leave a call (in which case any shared applications will continue to runbut will no longer be part of a sharing set)

shutdown the system (all current calls will be terminated and allapplications will become essentially unaware as part of the shutdownprocess)

launch an application

cancel an outgoing request if the callee is not responding

The user can also set various options, for example to indicate ifincoming calls are to be automatically accepted or rejected and howrequests for passive working are to be handled.

As shown in FIG. 15 the Call Manager user interface consists of a mainwindow, complete with action bar and client area, the latter containingan information area, which displays messages and other statusinformation, as well as context-sensitive prompts for the menupulldowns.

The actionbar provides the following options:

    ______________________________________                                        Call                                                                          New       start a new call                                                    Add       add person to call                                                  Hang Up   end the current call                                                Cancel    cancel and Add or New                                               Shutdown  end the Call Manager (and all calls)                                Share                                                                         Share     add an existing unshared application to the                                   current call                                                        Unshare   unshare an existing application from the                                      current call                                                        Launch    launch a new application                                            Options                                                                       Auto      answer automatically accepted                                       Passive   whether this machine may be used as a gateway                                 by others                                                           Sound     if ticked, then a "ring" accompanies                                          incoming calls                                                      Window                                                                        Log       displays or hides log view                                          Windowlist                                                                              list of all child views and log view                                Cascade   cascades the child views                                            Tile      tiles the child views                                               Arrange icons                                                                           arranges icons of child views                                       ______________________________________                                    

Other windows that can be displayed are the Unshared view, of awareapplications currently running which are not shared in a call, a Callview, a list of the nodes in a call, and for each node, a list of theshared applications which are running there, and Log view, which is aseparate window, not a child window of the control window, whichcontains a record of time-stamped events.

The Call Manager includes event handlers to handle call manager events,such as local application initialisation and named share requests fromother nodes.

Calls and Sharing Set

The concept of a call, as implemented by the Call Manager, has no realcounterpart in the subsystem. In essence, a call consists of one or morenamed sharing sets, sets of application instances which know about eachother. Each set consists of a single application that is running at eachnode within the call. The call manager itself is in one such sharing setfor each call. Only the Call Manager (and hopefully the user!) is awareof how the various sharing sets at a given node are grouped into calls.

Since a call consists of one or more sharing set, the various callmanager functions are in fact operations on sharing sets. Thus to starta new call to a remote node, the call manager creates a call name,typically by appending a numeric suffix to the node name, incrementingthe number after each call. It then attempts to share, using this name,with the call manager at the remote node. If the share is accepted, thecall has been established. To add a new node to an existing call, thecall manager merely tries to share with the call manager at the newnode, using the call name as the sharing set name. To join an existingcall from outside, the call manager merely tries to share with the callmanager at one of the nodes in the call, passing the the name of thecall to be joined. To leave a call, the Call manager unshares from theappropriate set. To add a new application into a call, the call managerissues shares on behalf of the application to each node in the call inturn, using the call name as the sharing set name. Note that once thereare applications in the call then each time a new node is added a sharewill be issued to it for each application.

There are six main states for the call manager, as shown in FIG. 17.These are starting, ready, connected, processing, ending, and resigning.Starting occurs from the point at which the engine is launched until ithas completed its initialisation. The engine then enters the readystate, waiting for commands from the user interfae of some otherapplication which has shared with the engine. Some of the events passedto the engine's event handler from the support system result in signalsbeing sent to the user interface component so that this in turn caninform the user and if necessary obtain a response which can be fed backvia a command to the engine. The engine enters the connected state assoon as a call is in progress, it returns to the ready state as soon asno calls are in progress. While in this state it will accept the sameset of commands as the ready state, with one exception, the shutdowncommand. The engine enters the processing state whenever it is waitingfor the user interface to respond or for a support system event tooccur. While in this state certain commands, such as call, are rejectedwith the "engine is busy" indication. Certain support system events,such as SHARE₋₋ REQUEST are also rejected.

The engine enters the ending state as soon as the NODE₋₋ SHUT₋₋ DOWN₋₋REQUEST event has been received and accepted. Note that the engine mustbe in the ready state for a shutdown to proceed, if any calls are inprogress, these must be terminated first. The engine enters theresigning state as soon as it has accepted a CALL₋₋ MANAGER₋₋ REQUEST.The state is similar to ending in that the engine will terminate, butthe rest of the support system will not. The engine will only resign ifit is in the ready state, if any calls are in progress these must beterminated first.

FIG. 16 shows 4 nodes, A, B, C and D. Node C is involved in two calls:

1. a call involving two application sharing sets, Y and Z and node D

2. a call involving a single application sharing set, X and nodes A andB

Call Manager Event Handling

The key events which the Call Manager handles are:

    ______________________________________                                        APP.sub.-- REGISTERED                                                                          this is raised when a (local)                                                 application issues the                                                        register.sub.-- app call                                     MONITOR.sub.-- EVENTS                                                                          in order to see both the local and                                            remote effects of an unshare, the                                             call manager must monitor                                                     these events.                                                PASSIVE.sub.-- LINK.sub.-- REQUEST                                                             this is raised when the system                                                wants to use resources at this                                                node to support the needs                                                     of other nodes                                               PASSIVE.sub.-- LINK.sub.-- RELEASE                                                             this is raised when resources                                                 at this node are no longer                                                    needed by the system to support                                               the needs of other nodes                                     SET.sub.-- CALL.sub.-- MANAGER                                                                 this is raised when another                                                   application issues a                                                          set.sub.-- call.sub.-- manager call                          SHARE.sub.-- REQUEST                                                                           this is raised when a request                                                 is received from another node                                                 to share with a named application                            SHARE.sub.-- REJECTED                                                                          this is raised when a local                                                   application refuses a share                                                   request (normally the result                                                  of some sort of error)                                       SHUT.sub.-- DOWN.sub.-- REQUEST                                                                this is raised when a request                                                 has been made, either by the                                                  user or by an application, for                                                the system at this node                                                       to be shut down.                                             SIGNAL           this is raised when an                                                        application issues a signal whose                                             target is either null or a name                                               rather than a handle                                         APP.sub.-- DEREGISTERED                                                                        this is raised when an aware                                                  application terminates                                       ______________________________________                                    

These events are handled as defined below

Register₋₋ app

The Call Manager makes a note of the name of the application which isstarting, adding it to the list of applications in the sharing set forthe appropriate call, or the unshared list, depending on which isactive. If a call is active and the application was started by the user,the Call Manager will issue a named share call to each remote node inthe call so that the application gets shared across the call. If theapplication was launched by the Call manager as a result of an incomingshare request, the Call Manager completes the share by issuing a localshare on behalf of the remote node/application.

When applications terminate, their names are removed from theappropriate list (see APP₋₋ DEREGISTERED below).

The Call Manager always returns RC₋₋ OK for APP₋₋ REGISTERED events.

PASSIVE₋₋ LINK₋₋ REQUEST

This event is handled in a straightforward manner. The Call Managerchecks the state of the Passive Working option. If it is permit, therequest is accepted, while if it is deny the request is refused. If itis ask, the Call Manager puts up a dialogue box asking the user if therequest is to be accepted (the panel displays as much information aboutthe request as possible) and then accepts or rejects the requestdepending on the users response (by returning RC₋₋ OK or RC₋₋ FAIL).

MONITOR₋₋ EVENTS

The two events that the Call Manager is interested in are the results ofan unshare call (raised locally) and an unshare event (raised remotely).The Call Manager reacts to them by removing the application from theappropriate list.

If the unshare comes from a remote call manager, this is indicating theyhave left the call, so the Call Manager responds by dropping them fromthe appropriate call list. In the case where there were only two partiesin the call (i.e. the call has effectively ended), the Call Managerunshares and moves any applications still listed as within the call tothe unshared list and then removes the call.

The Call manager returns RC.₋₋ OK for all events.

PASSIVE₋₋ LINK₋₋ RELEASE

This event is generated when the channels using the passive link aredestroyed. When it occurs, the Call Manager merely updates the mainwindow to indicate that the passive link is no longer present andreturns RC₋₋ OK.

SET₋₋ CALL₋₋ MANAGER

The Call Manager responds to this event by returning RC₋₋ OK, whichallows the transfer of the Call Manager role to the new application.

SHARE₋₋ REQUEST

The Call Manager looks at the name to be resolved. If this is the callmanager name, then this is really a request from a remote call managerto start a new call. The user info will contain the ID of the call (i.e.the ID assigned by the remote node). This is needed to resolve ambiguityin cases where the two nodes are involved in more than one call witheach other.

In this case, the Call Manager responds checking the state of the Answeroption. If it is manual, the Call Manager puts up a dialogue box askingthe user if the request is to be accepted (the panel displays as muchinformation about the request as possible). If it is auto-answer, therequest is accepted.

If the request is not from a call manager, it must come from a nodewhich is already a party to an existing call. Because of this, suchincoming share requests are always accepted. Note that the incomingshare request contains a call ID. This is because a given pair of nodesmay have more than one call in common and allows the resulting ambiguityto be resolved. To accept the share request, the Call Manager attemptsto launch the corresponding application. It looks in the LAKES.INI filefor an entry in the APPLICATIONS section whose KEYWORD matches thetarget application used in the share request. If none is found, an erroris reported. If an entry is found, the value in the profile entry isused to fill in the fields of a launch call, which is then executed. TheAPPLICATIONS section might look like this:

[applications]

chat=c:\lakes\apps\chat.exe, c:\lakeskwork, . . .

chalkboard=c:\lakes\apps\chalk.exe, c:\lakes\work, . . .

filetransfer=c:\lakes\apps\xfer.exe, c:\lakes\work, . . .

The Call Manager makes a note of the handle of the launched program, sothat when the corresponding Register₋₋ app event occurs it doesn't tryto share it again (see the APP₋₋ REGISTERED event above). If the launchfails, then RC₋₋ SHARE₋₋ REJECTED is returned. One the other hand if thelaunch is successful, the Call Manager returns RC₋₋ SHARE₋₋ NO₋₋CONFIRM. When the launched application later issues register₋₋ app, theCall Manager will issue a share call and the application should thenreturn RC₋₋ SHARE₋₋ CONFIRMED.

Note that the Call Manager described here never resolves an incomingshare request by sharing with an application that is already running--anew instance is always launched.

SHARE₋₋ REJECTED

As noted above, an application launched by the Call Manager will, onceit has registered, be the target of a share issued by the Call Manager.

Normally, it should respond with RC₋₋ SHARE₋₋ CONFIRMED since the CallManager has already accepted the call. In tile case where an applicationcannot accept a share (for example, due to lack of resources), therejection will be sent to both the Call Manager and the original remoteapplication. The Call Manager responds by "forgetting" the originalshare and returning RC₋₋ OK.

SHUT₋₋ DOWN₋₋ REQUEST

The Call Manager responds to this event by returning RC₋₋ OK, whichallows the shutdown to continue. This will in turn cause allapplications (including the Call Manager) to receive a SHUT₋₋ DOWNevent, when the system is actually shutting down. Like the othersupplied applications, the Call Manager reacts to this event byde-registering.

SIGNAL

Two types of signal will cause a SIGNAL event to be raised in the CallManager:

1. a signal whose target₋₋ application parameter is null. Such eventsare treated as Call Manager commands

2. a signal whose target₋₋ application parameter mentions an applicationby name rather than by handle. The Call Manager resolves the name by

checking if an application of that name is currently running (i.e. anregister₋₋ app has been issued which uses that name)

if so, the signal is transferred to that application (if there areseveral, the signal goes to the first instance)

if there are none, the Call Manager does not launch a new instance.Instead the signal is ignored.

APP₋₋ DEREGISTERED

This event is generated when an application terminates. The Call Managerresponds to this event by removing the name of the de-registeringapplication from the appropriate call list, updating the main windowappropriately and returning RC₋₋ OK,

A Simple Example

One possible sequence of events is as follows:

1. user A calls user B (resulting in the sharing of call managers)

2. user A starts chat application (which will be shared by A's callmanager and thus launched by the call manager at B, forming the firstapplication sharing set)

3. users A and B chat for a while, then user B terminates the chatapplication (which ends the sharing set). Although the chat applicationcontinues to run at A, it appears on the unshared list as it no longerpart of the call.

4. user B starts the chalkboard application. Since the two users arestill in a call, the call manager at B will issue a share, and thus A'scall manager will launch the chalkboard there, forming a new sharingset.

5. user A hangs up the call.

Looking at this sequence at the API level, we would see something likethe following:

1. The Call manager at A starts the process by issuing a share with B.At B, the Call Manager will note that the share involves the callmanager (and is therefore asking to set up a new call). Assuming thecall is to be accepted, the call manager accepts the share between callmanagers.

2. When the user at A starts the chat application, the call manager at A(which sees the register₋₋ app event) will issue a share. At B, the callmanager will accept the share request by issuing a launch for thecorresponding application.

3. When user B terminates the chat application, there will be anautomatic unshare issued by the subsystem at B. Since both call managersare monitoring unshare calls and events, they will both be notified ofthe unshare and can thus update their call lists. The call manager at Bwill see the unshare call and the call manager at A will see the unshareevent.

4. The chalkboard application is processed in the same way as the chatapplication.

5. Finally, the user A hangs up, the call manager at A will issue anunshare, so ending the call.

Structure of a Well-Behaved Application

One of the main aims of the Call Manager design is to simplify thestructure of an aware application. Since the Call Manager looks aftermaking a call, issuing share and unshare calls and so on, a typicalapplication need only:

register₋₋ app at start up. If the return code indicates no call manageris present, the application should inform the user and then terminate.

after registering successfully, use create₋₋ ports to establish achannel to itself (for most applications a merged channel set will beused)

allow most events to be handled in the default way

when asked to terminate, first remove₋₋ ports, then optionally unshareand then deregister₋₋ app

It is not normally necessary for an application to issue either share orunshare since the Call Manager will handle these,

As far as events are concerned, most can be handled in a default way.For example:

SHARE₋₋ REQUEST should result in SHARE₋₋ CONFIRMED being returned, sincethis event is the result of a local share from the Call Manager whichhas already decided to accept the call. There is no need to do any otherprocessing.

SHARE₋₋ CONFIRMED should result in RC₋₋ OK but can otherwise be ignored.

SHARE₋₋ REJECTED should not occur (since all SHARE₋₋ REQUESTs should beaccepted).

SHUT₋₋ DOWN should result in RC₋₋ OK and the application should theneither terminate (in an OS/2 PM environment by posting a WM₋₋ QUITmessage to itself for example) or at least no longer issue API calls.

UNSHARE should result in RC₋₋ OK but can otherwise be ignored.

We claim:
 1. A programmable workstation for collaborative working in anetwork in which workstations represent nodes of the network, thenetwork being connected by physical links for supporting communicationsbetween nodes, each node including an operating system and applicationprograms, and potentially having at plurality of call manager programsresponsible for handling incoming communications which are not specificto a particular application program instance running at the node,wherein only one call manager can be active at a node at any giventime;the workstation comprising: a network control program layer,running on the operating system, for controlling physical routing ofsaid communications between nodes; and a collaborative applicationsubsystem for interfacing with the application programs running on theworkstation, said collaborative application subsystem being responsiveto a predetermined application program call from a call manager programrunning on the workstation to establish that call manager program as theactive call manager program at the node to handle incoming events whichare not specific to any application program instance at the node.
 2. Aworkstation as claimed in claim 1 in which, if a call manager is alreadyactive at the node, the predetermined application program call isdirected to the currently active call manager which, at its option, maytransfer handling of incoming events to the call manager from which saidpredetermined application program call originated.
 3. A workstation asclaimed in claim 1 or claim 2 in which incoming communications which arespecific to an application instance are passed directly to thatinstance.
 4. A workstation as claimed in claim 1 or 2, wherein the callmanager in response to an incoming non-application specific event passedto it by the collaborative application subsystem naming an applicationprogram, directs the event to an existing instance of the namedapplication, launches a new instance of the named application or handlesthe event itself.
 5. A method of collaborative working in a network inwhich programmable workstations represent nodes of the network, thenetwork being connected by physical links for supporting communicationsbetween nodes, each node including an operating system and applicationprograms and potentially having a plurality of call manager programsresponsible for handling incoming communications which are not specificto a particular application program instance running at the node,wherein only one call manager can be active at a node at any given time,each workstation including a collaborative application support systemfor interfacing with applications running on the workstation, the methodcomprising:receiving, at the collaborative application support system, apredetermined application program call from a call manager programrunning on the workstation, and establishing, responsive to saidpredetermined application program call, the call manager program asbeing the active call manager at that node responsible for handlingincoming communications which are not specific to any applicationprogram running at the node.
 6. A method as claimed in claim 5 in which,if a call manager is already active at the node, the predeterminedapplication program call is directed to the currently active callmanager, which, at its option, may transfer handling of incoming eventsto the call manager from which said predetermined application programcall was received.
 7. A method as claimed in claim 5 or claim 6 in whichincoming communications which are specific to an application instanceare passed directly to that instance.
 8. A method as claimed in any oneof claims 5 to 6 in which the call manager responds to an incomingnon-application specific event naming an application program bydirecting the event to an existing instance of the named application,launching a new instance of the named application or handling the eventitself.